Aerial mine



Feb. 8, 1944. J. A, BARKLl-:Y

AERIAL MINE 2 sheets-sheet 1 AF'iled May l5. 1941 'IIIIIIIl Feb. 8,1944. J. A. BARKLEY 2,341,351-

AERIAL MINE Filed'May 1S, 1941 2 sheets-sheet 2 TDME DELAY CONTROLPatented Feb. 8, 1%44 v artist MINE Joseph Amos Barkley,Silvercroft-,Del. l Application May is, 1941, serial Nassasiv 1 o1aim.'-'(ci. 1oz-9) This invention relates to aerial mines, and moreparticularly, to a mine adapted to operate at a given height above theearth and to explode in response to sound waves or vibrations from asource, such as a hostile aircraft, in predetermined proximity to themine.

An important object of the invention is the provision in a mine of thischaracter of means for preventing response of the mine to extraneousdisturbances, such as the explosion of anti-aircraft fire.

A further object of the invention is to provide a constructionpreventing response'of the mine to even those vibrations to which it issensitive until it has reached a predetermined height above the terrainfrom which itis launched. I

A still further object of the invention is the provision of meanswhereby the mine will be maintained at all times at a predeterminedlevel.'

Another object of the invention is the provision of means whereby themine will only explode upon an approach thereto by the aircraft which itis designed to destroy within certain limits. y

A further object of the invention is the inclusion in the structure ofcertain safety devices precludlng accidental detonation of the mineduring launching or landing thereof.

Other objects and advantages of the construe tion will become obviousthroughout the course of the following description.

In the drawings, wherein for the purpose of illustration I have shown apreferred form of my invention,

Fig. l is a pictorial representation of the use of mines constructed inaccordance with my invention;

Fig. 2 is a` vertical sectional view through the mine unit;

Fig. 3 is' a vertical mine unit taken at Fig. 2;

Fig. 4 is a side elevation of the mine unit;

Fig. 5 is a detail sectional view of the baromesectional view throughthe right angles to the view of tric switch partially in section of onemodiable gas-inflated supporting balloon which may be employed eithersingly or in multiple with the mine unit hereinafter to be described.This balloon element is equipped with means whereby it will move toaselected height and remain at that height. This may be accomplished,for example, by providing the balloon Iwithan outlet neck Ii, the upperend of which aords a seat for a springseated check valve I2 preventingthe escape of the supporting gas therefrom. As at present shown, thischeck valve is connected toa remote portion of the balloon, indicated atI3, byA the flexible element I6, with the result that when the balloondistends beyond a predetermined diameter, as it will when `it reaches asufficiently rareed atmosphere, the flexible element iii will lift thevalve i2 from its seat, permitting release of a portion of the contentsuntil the balloon is restored to its predetermined maximum size. Sincethe rarecationof the atmosphere may be at least generally said to beproportional to the distance from the earth, such an arrangement willserve to maintain the balloon at an approximate selected altitude. Byadjusting the length of element I6 and the amount of gas in the balloon,the maxlmurnaltitude can be regulated.

Suspended from the balloon,` as by means of ilexible element I5, is amine unit I6. Preferably a parachute I5a is attached to the mine unit soas to lower the same gradually in the event that the balloon shouldburst. Unit I6 comprises an upper casing element I1 at present shown asadapted to receive the explosive (see Figs. 2 and 3), and a lower casingelement I8, detachable from the casing element i i as by means ofquickdetachable fasteners indicated at i9, and at present shown asspring plates rotatable about' pivots 20 and engaging pins 2| carriedbythe elements I8. The bottom casing element I 8 carries, preferably atits lower end. a series of vibrationreceiving horns or sound collectors22. This element likewise affords a housing for the electrical controlapparatus 23 including a sensitivity control 26 which may be adjustedthrough an externally disposed knob 25 and a time delay control 59similarly adjustable by knob 62.

In addition to affording space for the electrical control apparatushereinafter to be more fully described, the element I8 likewise houses abarometric switch 2o. Switch 26 (see Fig. 5) cornprises a closed chamber2l, one vface of which is in the form of a flexible diaphragm 28carrying the switch contact 29. The chamber 27 is bodily adjustabletoward and away from one wall of the element i8 by means of a screw 30rotatably iounted in this wall and having at its outer end n adjustingknob 9i. The contact 29 of diahragm 29 is opposed by a contact 92 on themer end of a screw 33 adjustable through the ame wall as that mountingthe screw III and conrollable through a knob 94 coacting with a suitbiedial 35 (see Fig. 4) which may be coneniently graduated in thousands offeet.

The electrical control apparatus is connected to detonator 99 and to aswitch 21 by means of ack sockets 39 and associated jack plugs on umperconnections 39. The ,detonator is renovably held in a receptacle 40within the exploive chamber I1 by means of a clip 4I. A pair .f jacksockets 42 are disposed adjacent the jack ockets 38 for a purpose whichwill be described ater. It will be noted that the detonator is luicklyremovable merely by operation of clip II and removal of the jack plugselectrically coniecting it to the other elemen Moreover, the entireexplosive charge may be quickly sepa- .'ated from the rest of the minesimply by de- ;aching section I1 from section I8.

The voltage produced by the vibration-respon sive device 45 may besupplied to a step-up transformer 59 which is preferably peaked to thefrequencies above mentioned. The voltage across the secondary oftransformer 50, or a portion thereof, is supplied `to an electron tubeamplifier which may comprise/as many cascaded stages as may be desired.The sensitivity control device 24, previously referred to, may take theform of a potentiometer interposed between transformer 50 and the ilrstl,ube 5I. as illustrated, and serving to control the sain of theamplliler. Tube 5I may take the form of a simple triode, as illustrated,or it may take any other suitable form. In the speciilc circuitillustrated, tube 5I is coupled to a diode-triode tube l2 by means of atransformer 53, which is also preferably peaked to the desiredfrequencies. A by-pass condenser 6I serves to control the frequencyresponse. This condenser may have a l capacity of about .002 microfarad.Tube 52 serves The switch 91 is normally biased to its open position, asshown in Fig. 2, for example by the resilience ol' arm 43 and the weightof hook 44 secured thereto. By means of the hook, the flexible elementof the sustaining balloon or balloons is connected to the mine. Thuswhen the element I5 is not under tension, i. e., when the balloon is onthe ground or in the event that the balloon bursts while in the air, theswitch 31 is opened and prevents explosion of the mine. When the weightof the mine is sustained by the balloon, switch 31 will be closed.'I'his will, of course, occur immediately upon proper inflation of andrelease of the balloon, and, under ordinary circumstances, the minewould then be ready for detonation. Any possibility of such detonationis, however, prevented through the barometric switch 2B which, prior torelease of the balloon, is set to prevent closure of such switch untilthe balloonA has reached a predetermined elevation above the terrainfrom which it is released.

Referring now to the electrical system illustrated in Fig. 7, there isprovided a suitable vibration-responsive device 45 which isarranged toreceive the sound vibrations collected by the collectors 22. This devicemay take any suitable form, for example, it may comprise one or morevibrative reeds 46 and an associated electromagnet 41 forming a simpleelectric generator, as will be well understood. This device serves, ofcourse, to translate the vibrations received by the vibrative element 46into electrical currents. The vibrating reeds may be designed andarranged to vibrate over a predetermined frequency range. By mountingthe reed or reeds in rubber, or by damping the reeds in any suitablemanner, a wider frequency response range may be obtained.

It will be apparent that the device 45 may take other well-known forms;for example, it may take the form of a. microphone. In any case, thisdevice should be designed so that it has a resonance frequency orfrequencies of vibration within a predetermined frequency rangeincluding the noise or sound frequencies commonly produced by aircraft.

A common battery energy in the circuit also serve to energize tron tubesemployed. trois the energiz'ation of the apparatus.

48 may serve as a source of of the device 45, and may the laments of theelec- A manual switch 49 con- 'nsi to control a relay 54, which in turncontrols -the energization of the detonator 36, as will be describedpresently. If desired, suitable iilters 55 and 55 may be connected asillustrated in order to further improve the frequency response of thecircuit, and each iilter maycomprise an adjustable resistor andcondenser.

While it is preferred to employ the diode-triode tube 52 for reasonswhich will be apparent later, it is within the contemplation of theinvention to employ any suitable single or multistage amplier. Moreoverany suitable type of interstage coupling may be employed; for exampleresistance-capactance coupling could be used.

The diode-triode 52 is arranged so that it is normally inoperative orquiescent, and it is adapted to be triggered by incoming vibrations,provided such vibrations are of a sustained nature and are not merely ofa transient nature. To this end, the triode section of the tube isbiased substantially to plate current cut-off by means of a biasingsource 51. The diode rectifier circuit is connected to the control gridof tube'52 through a condenser 58 and a variable resistor 59. Therectified voltage appearing in the rectier circuit is thus impressed oncondenser 58 through variable resistor 59 which controls the rate atwhich the condenser is charged by the said voltage.

Condenser 58 may have a capacity of about 8 microfarads, while resistor59 may have a resistlance of about one megohm. A resistor 60 which isalso of very high resistance slowly discharges the condenser. Thecondenser-charging voltage is polarized in opposition to the negativebias voltage on the grid of tube 52, and, therefore, when the condenserbecomes suillciently charged, it overcomes the negative bias and causesplate current to iiow in the triade section .of tube 52. It will beapparent that by varying the resistance 59, the time delay or timerequired to charge the condenser 59 may be varied. By this arrangement,the circuit is caused to discriminate between sustained vibrations andvibrations of short duration, and the discriminating action may bevaried by means of resistor 59. Continuous or sustained vibrations willcause the condenser 59 to accumulate a charge until it triggers thetube, whereas transient vibrations will not charge the condensersuiiciently to trigger the tube and any charge due to such vibrationswill be dissipated by resistor 60. Thus, the device is caused to operatein response to the sustained vibrations produced by approachingaircraft, and at the same time it is prevented from responding tovibrations of short duration such as may be caused by antiaircraft lire,the explosions of nearby mines, etc.

It will be apparent also that the circuit may be designed and adjustedto operate at a predetermined noise level corresponding to predeterminedproximity of an aircraft. Obviously any desired threshold level may beestablished by the tube bias and the condenser.

The employment of the particular circuit illustrated also conserves theplate supply battery,

since the tube 52 is non-conductive except when' it is triggered.

Since the switches 26 and 31 will have been previously closed, asdescribed above, the energization of relay' 54 completes an energizingcircuit for the detonatorASB which may be energized `from the platesupply source 62. The detonator, when thus activated, causes theexplosion of the explosive material within the chamber I1.

In order to assure proper operation of the baronetric switch 26 and tocompensate for surface elevation and local barometric conditions, this;witch may be pre-adjusted in the manner now '.o be described. The jackplugs are removed from lack sockets 38, and a special jack plug 63, as:hown in Fig. 8, is inserted in the jack sockets 38 ind 42. The prongs64 of this plug are connected iogether and serve to bridge sockets 42,while the rongs 65, which are received by sockets 38, are :onnected to avoltmeter or a lamp 66. It will be :een that this disconnects theVdetonator 38 and he switch 31 and places the voltmeter, or lamp, ncircuit with the battery 62 and the barometric witch 26. The handle 34is set to zero altitude, nd the zero adjustment knob 3| is rotated in alirection to close the contacts of the barometric witch which will beindicated by the lamp or 'oltmeten This adjustment establishes theconact 29 in proper position for zero altitude. 'I'he :nob 34 is thenturned until it indicates the altiude at which it is desired that thebarometric witch shall close. This adjustment, of course, stablishes thecontact 32 at a. certain distance rom contact 29.

It will be apparent to those skilled in the art hat other forms oftrigger type control circuits ray beemployed. For example, in Fig. 9there sshown another form of such a circuit employing gas lledionic-cathode glow-discharge tube 63 commonly known as a gas triggertube. The voltage across the secondary of transformer 53 is applied to asuitable rectifier, such as the oxide rectiiier 64. The rectied voltageis applied to condenser 58 which is connected to the starter grid of thegas tube. The starter grid may be maintained at a potential Just belowthe trigger potential of the tube by means of the tap on battery 62. Thevoltage on condenser 58 is polarized the same as the potential appliedto the grid.

In response to sustained vibrations the condenser 58 will acquire |acharge sumcient to trigger the tube, causing plate current to iiow andthereby energizing relay 54. Transient vibrations, however, will notcharge, the condenser suiliciently to trigger the tube, and the resistor60 will dissipate any charges due to such vibrations.

Aside from the above-noted differences, the circuit of Fig. 9 is similarto that of Fig. l and operates in the same manner. It should be noted,however, that in theuse of the gas tube it may ibe unnecessary toamplifythe voltage generated by device I5, as such voltage may be suflicient totrigger the tube, but it is desirable to employ one or more stages ofamplication.

From the above description, it will be seen that the invention providesa novel Iaerial mine having various novel features. It will beunderstood. of course, that the invention is not limited to the specificstructure illustrated, but is capable of various modiilcations withinthe scope of the appended claim.

I claim:

In an aerial mine, an elevating balloon, la mine unit, means forsuspending said unit from said balloon, detonating means for explodingthe mine, an electrical energizing circuit for said detonating means,vibration-responsive means for closing said energizing circuit, anormally open safety switch included in said circuit and operable bysaid suspension means to closed position whenever sad unit is lifted bysaid balloon, and a normally open barometric switch included in saidcircuit serially with said safety switch and operable by predeterminedatmospheric pressure to closed position when said unit is lifted by saidballoon to a predetermined altitude.

JOSEPH AMOS BARKLEY.

